The medical device industry produces a wide variety of electronic devices for treating patient medical conditions. Depending upon medical condition, medical devices can be surgically implanted or connected externally to the patient receiving treatment. Medical professionals or other clinicians use medical devices alone or in combination with drug therapies and surgery to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life. Examples of implantable medical devices designed to deliver therapeutic electrical stimulation include neurological stimulators, pacemakers and defibrillators.
Implantable medical devices configured to deliver therapeutic electrical stimulation commonly deliver therapy via electrodes positioned on one or more leads operatively connected to the implantable medical device. In some instances, the housing of the implantable medical device may also serve as an electrode or an electrode may be positioned on the housing of the implantable medical device. The electrode or electrodes are commonly positioned in the patient's body during the same surgical procedure in which the implantable medical device is implanted. Sometimes the electrode or electrodes are placed in a follow-up procedure.
The positioning of electrodes, and associated leads, is often an inexact procedure and may commonly be dependent on the particular physiologic characteristics of the patient. In addition, electrodes may commonly be positioned within the patient without the medical professional or user conducting the procedure being capable of actually seeing where the electrodes are positioned. Instead, external aides such as fluoroscopes and/or endoscopes may commonly be employed to inform the medical professional or other user as to an approximate location of the electrodes. Electrodes may also be placed by stereotactic head frame which allows placement of the lead without direct visualization. Further, the ideal target is often not known a priori and time constraints may not allow for perfect targeting in the operating room.
Due to the inherent uncertainty involved in the placement of electrodes for an implantable medical device, implantable medical devices and the external controllers that interface with the devices are commonly operable to perform a test on the leads and electrodes to verify that the leads and electrodes are functioning properly and are positioned correctly. A common test is to check the impedance between pairs of electrodes. During testing, an electrode can be driven with a signal having known electrical characteristics. The signal may be measured, e.g., on another electrode or electrodes, and the impedance computed between electrodes using known fundamental relationships. The measured impedance value can give a medical professional or other user information relating to whether the electrodes involved in the test are positioned correctly and operating properly.
An external controller, e.g., a physician programmer, is commonly utilized in lead impedance tests. Physician programmers can be similar in size and composition to a large laptop computer. The physician programmer provides a user interface via a display screen, and is manipulated by a medical professional via a variety of inputs, such as buttons and touchscreens. The physician programmer commonly communicates with the implantable medical device via inductive telemetry. In order to accomplish this, a coil, operatively coupled to the controller, typically by a wire, is placed over a coil operatively coupled to the electronics in the implantable medical device producing an alternating current in the coil operatively coupled to the controller, thereby establishing an inductive link over which data may be passed in either direction. Because physician programmers are typically not sterilized, the physician programmer itself is placed outside of the sterile field, only the coil and its housing is taken inside the sterile field, e.g., using a sterile bag.
For example, United States Patent Application Publication No. 2006/0036186, Goetz et al, Automatic Impedance Measurement of an Implantable Medical Device, discloses a method and controller for automating impedance measurements. An entry for each electrode pair is displayed on a user interface. Each electrode pair entry includes an identification of electrodes for an electrode pair, an associated value of impedance and a value of current that is measured between the electrodes of a pair.
In another example, U.S. Pat. No. 5,891,179, Er et al, Method and Apparatus for Monitoring and Displaying Lead Impedance in Real-Time for an Implantable Medical Device, discloses a method and controller for displaying real-time graphical representations of variable lead impedance. Impedance values are calculated using Ohm's law or other related equations. The calculated impedance values are then output to a graphic display for presentation in graphical form or are output to a graphic printer, or both.
In another example, United States Patent Application Publication No. 2003/0114899, Samuelsson et al, Programming System for Medical Devices, discloses a method and controller for displaying graphical representations of a quantity influenced by the operation of a medical device. Such quantities may include information derived from tests and diagnostics, such as an electrode impedance test.
In another example, United States Patent Application Publication No. 2005/0033385, Peterson et al, Implantable Medical Device Programming Apparatus Having a Graphical User Interface, discloses graphical displays of the operation of a medical device, such as a test of a device lead. Results are organized according to the anatomical position of the lead, i.e., whether the lead is an atrial or ventricular lead, allowing the clinician to efficiently assess the functionally of all lead data by virtue of its grouping into precise anatomical categories.
In another example, U.S. Pat. No. 6,721,600, Jorgenson et al, Implantable Lead Functional Status Monitor and Method, discloses a system for obtaining trend data on the status of leads of an implantable medical device. The lead status measurement derives its data from various sources including lead impedance, non-physiologic sensed events, percentage of time the device is in mode switch, the results of capture management operation, sensed events, reversion paced counts, and refractory sense counts. The lead status measurement employs a set of weighted sum rules used by algorithms to process data from all of the above-mentioned sources to arrive at easily interpreted messages accessible to clinicians via an external programmer. Data from these sources identify lead conductor/connector interface issues and electrode/tissue interface issues indicative of lead-related mechanisms suggestive of impending or actual lead failure. The weights are “interpreted” for the user in the following manner either by indicating (1) lead-related parameters are all within range or operating normally; (2) one or more of the lead parameters are out-of-range and, thus, leads should be investigated; or (3) a number of lead parameters are out-of-range and a safety problem exists.
Messages to the user refer to three types of lead-related conditions: either lead/conductor/connector messages, lead insulation messages or biological interface messages. Examples of such messages include: (1) high impedance (>4000 ohms, 2× increase over reference, among others); (2) increase in threshold(s) above preset or programmed limit; and (3) reduction in R-wave and P-wave amplitude below preset or programmed limits.
Summary information from a variety of trend data is therefore presented for the use of a medical professional.